MD/PA, it's usually either US 15 (if visiting friends in Harrisburg area)
or US 1 if visiting family in far northern Delaware, or friends in extreme southern PA (this is my scenic and slightly afield "shunpike and also avoid I-95 in Delaware south of Wilmington" route).
Very rarely, I-70 -- used to do this more often when I was doing more pleasure driving.
MD/DE, if shunpiking but wanting to go to Newark for some reason, MD/DE 279 or MD/DE 273.
MD/VA, most of the time it's I-495 at American Legion Bridge north of DC. Also US 340 if heading in that general direction (even to much further destinations) but not at the present time due to the closure.
MD/DC, very rare occurrence nowadays, but usually it's MD 185/Connecticut Avenue.
MD/WV directly -- extremely rare for me now. The ones I've used most often are US 522 at Hancock, or I-68, but I rarely go out there anymore.